1. Field of the Invention
The present invention is directed to a telephone switching system, particularly a CENTREX (CTX) telephone switching system, in which CTX connections or CTX calls can be setup between defined CTX subscribers.
2. Description of the Related Art
CENTREX systems are purely software solutions that implement private branch exchanges connected to the public telephone network. CENTREX (CTX) groups can be used to replace hardware-implemented private branch exchanges (PBX) within each fixed network exchange (local exchange LE) of the public telephone network (public switched telephone network, PSTN). The advantage of this software CTX solution is that it allows the telephone terminal equipment previously employed for realizing private branch exchanges to continue to be employed, allowing a flexible adaptation/modification of the individual CTX groups. The subscribers of a CTX group (CTX subscribers) are directly connected to the respective exchange but have the feeling of belonging to a private network.
Specific CTX functions are offered to the CTX subscribers of a CTX group for the setup of CTX connections or for the switching of CTX calls; these functions are essentially similar to those functions that a subscriber connected to a hardware implemented private branch exchange is accustomed to. These CTX functions can comprise a private telephone number plan for the CTX subscribers, the selection of an operator, call redirection, call forwarding, implementing the exit code for exiting into the public network, and other functions. Furthermore, CTX additions beyond the standard functions or features are conceivable, such as call redirection which may be dependent on whether a call is internal to the group or comes from outside the group or is dependent on traffic restrictions (for example, blocking for calls from or into the public telephone network).
The CTX groups of a plurality of switching centers can form an overlapping CTX private network. An expanded ISUP signaling between the affected switching centers is employed for the control of the CTX functions that are offered in order to be able to transmit control information, such as the type of call or other features or functions (e.g., blocking).
The right-hand section of FIG. 6 shows a simplified block circuit diagram of a known realization of a CTX system. In particular, FIG. 6 shows a fixed network exchange 15 to which a wired or stationary CTX subscriber 8 is connected, All information required for CTX call processing are deposited in a data bank. This data bank comprises a CTX-specific subscriber database 13 as well as a CTX-specific group database 14. Information about the CTX subscribers are deposited in the CTX-specific subscriber database, such as internal telephone numbers, external/public telephone numbers or CTX functions that are available to or, respectively, usable by the respective CTX subscribers.
Information about the individual CTX groups are stored in the CTX-specific group database 14, which contains; among other things, a group number plan or predetermined group functions deposited in it that are available for the subscribers of the respective CTX groups.
Additionally, a traditional database 12 is provided for depositing the standard fixed network information that are required for call switching via the respective switching center 15. This database 12 thus comprises generally public data, such as a number plan or a listing of the connected subscribers. A controller 9, which is expanded by a control unit 10 for CTX-specific call processing, is provided for processing calls to be switched via the switching center 15. This controller accesses the databases 12 through 14 via internal interfaces 11 in order to setup connections or to switch calls dependent on the information, stored in the respective database. In particular, the CTX control unit 10 accesses the two CTX-specific databases 13, 14 and is exclusively responsible for processing CTX calls.
The left-hand section of FIG. 6 shows a simplified block circuit diagram of a traditional mobile radio telephone system. A mobile radio telephone terminal equipment 1 communicates with a mobile radio telephone base station 2 (BS) that is allocated to a mobile switching center (MSC) 3 of a public mobile radio telephone network (public land mobile network PLMN). The mobile switching center 3 comprises a controller 4 for processing mobile radio telephone connections to the mobile terminal equipment 1. This controller 4 accesses a temporary database 6 in which information about mobile subscribers is deposited, via internal interfaces 5. This database comprises what is referred to as the visitor data file (visitor location register VLR) of the mobile switching center 3; it may be utilized in GSM mobile radio telephone networks for supporting subscriber mobility.
Additionally, a permanent database 7 is provided that likewise stores information of the mobile subscribers contains the home data file (home location register (HLR)) in GSM mobile radio telephone networks. The visitor data file is coupled to the home data file of the mobile switching center 3 in order to be able to unambiguously identify the momentary location of a mobile subscriber. A home data file in which the mobile subscriber is registered is allocated to each mobile subscriber 1.
When, however, the subscriber 1 is located outside the coverage area of the mobile switching center 3 allocated to him (e.g., when located abroad), it is determined that the corresponding mobile subscriber is not registered as a subscriber of the mobile switching center 3. This determination is made after initially contacting the corresponding mobile terminal equipment 1 with the base station 2 allocated to the mobile switching center 3. The mobile switching center having the corresponding home data file originally allocated to the mobile subscriber 1 is subsequently informed (via the fixed network) that the mobile subscriber is currently residing in the area of the new mobile switching center. Information that are necessary for encryption (among other things) are stored in the visitor data file of the new mobile switching center.
When the mobile subscriber 1 located outside the coverage area of his mobile switching center is called, a determination is made on the basis of the entry in his home data file that the called mobile subscriber is located in the area of the new mobile switching center and the connection is through-connected to him.
It can be particularly seen from the illustration of FIG. 6 that completely different executive sequences for call processing as well as databases were previously provided for mobile subscribers 1 and CTX subscribers 8. A parting wall that has not yet been satisfactorily overcome exists between the mobile radio telephone network shown at the left side and the fixed network with CTX subscribers shown at the right side, since mobile subscribers are not bound to a specific switching center, so that the CTX solution based on switching centers for a stationary CTX subscribers cannot be transferred without further effort to mobile CTX subscribers.
Although the field of intelligent network (IN) provides known solutions that combine wired or stationary subscribers with mobile subscribers, CTX functions can only be partially simulated utilizing such intelligent networks. A complete utilization of the entire scope of CTX functions, such as the billing according to reduced fee schedules for private networks, is not possible.
Additionally, a relatively complicated adaptation of the central TN network A element referred to as xe2x80x9cservice control pointxe2x80x9d (SCP) as well as an administration of the individual subscribers in the switching centers and this central IN network element is required given such IN solutions.
Furthermore, it is already known to forward calls from a CTX switching center, i.e., from the switching center 15 in FIG. 6, into the public mobile radio telephone network (PLMN).
The disadvantage of this method, however, is that this relates exclusively to call forwarding into the public mobile radio telephone network and does not additionally relate to the setup of connections in the opposite direction. This system can only be applied for the incoming reachability under the internal group telephone number and results in a detrimental call routing.
It follows from the above description that it has not formerly been possible to satisfactorily link mobile subscribers into a CTX group or into a CTX private network.
The present invention is therefore based on the object of allowing the involvement of mobile subscribers in CTX systems, particularly where the exchange-based CTX solution can continue to be employed for stationary CTX subscribers.
According to the present invention, this object is achieved by a telephone switching system comprising a CTX group that has wired CTX subscribers and mobile CTX subscribers, within which CTX connections can be setup, a database for storing CTX-specific data of these wired and mobile CTX subscribers, a fixed network switching center to which the wired CTX subscribers are allocated, where the fixed network switching center comprises a CTX-specific fixed controller for controlling the setup of a CTX connection via the fixed network switching center between a wired CTX subscriber and another CTX subscriber on the basis of CTX-specific data stored in the database, a mobile switching center to which the mobile CTX subscribers are allocated, which comprises a CTX-specific mobile controller for controlling the setup of a CTX connection between a mobile CTX subscriber and another CTX subscriber, and a data interface for the transmission of CTX-specific data between the fixed network switching center and the mobile switching center, where the data interface is comprised by elements of the fixed network switching center and the mobile switching center.
According to the present invention, a message interface for the transmission of CTX-specific information is established between the mobile switching center of the public mobile radio telephone network and the CTX fixed network switching center of the public telephone network, so that the CTX-specific databases of the CTX fixed network switching center can be made externally accessible for the mobile switching center.
Additionally, the controller of the mobile radio telephone switching center that is provided for the mobile call processing is supplemented by a CTX-specific controller that is provided for the CTX-specific mobile call processing. This CTX-specific controller of the mobile switching center can, for example, request CTX-specific information from the CTX fixed network switching center via the previously mentioned message interface, which are subsequently employed for the setup of a CTX connection between a mobile CTX subscriber and a further CTX subscriber of the corresponding CTX group. These CTX information can be requested and transmitted accompanying both a connection control as well as accompanying a location registration for the corresponding mobile CTX subscriber.
According to an exemplary embodiment of the present invention, the VLR part of the mobile switching center of the public mobile radio telephone network, i.e., the visitor data file of the mobile switching center, is supplemented by the possibility of accepting or of storing CTX-specific data. This VLR part thus serves as a temporary CTX-specific mobile subscriber database, so that the access to the CTX-specific data relevant for the mobile switching center can be accelerated. The acceptance of the data in the VLR part can likewise ensue accompanying the location registration at a new mobile switching center.
Furthermore, the HLR part of the public mobile radio telephone network, i.e., the home data file of the mobile switching center, can be supplemented by data that identify the affiliation of a mobile CTX subscriber to a CTX group. The HLR part in this case thus serves as permanent CTX-specific mobile subscriber database, whereby the data stored within serve as trigger for starting the CTX activities and for addressing the respectively responsible CTX fixed switching center. For starting the CTX activities, the CTX-specific data of the mobile subscribers deposited in the HLR part are loaded into the VLR part, this being accessed by the CTX-specific controller of the mobile switching center for setting up a CTX connection.
Real private branch exchanges, i.e., private branch exchanges realized in terms of hardware, can also be involved in the telephone number plan of CTX groups. An internal traffic with mobile subscribers in the same CTX private network is thus also possible for private branch exchange subscribers.
The advantage of the present invention is based on the idea that mobile subscribers can be simply classified into CTX groups or into a CTX private network, particularly where the mobile CTX subscribers are handled largely like wire-bound CTX subscribers in view of the establishment of the CTX group data and the CTX subscriber data. The CTX-specific databases in the CTX fixed network switching centers can also be employed largely unmodified for mobile CTX subscribers.
By contrast to the solution initially described employing intelligent networks, no additional network components are required in the present case, such as the SCP network element (given an intelligent network) being required in the participating networks (i.e., in the public mobile radio telephone network (PLMN) and the public fixed network (PSTN)).
The switching of CTX calls, i.e., the routing, can be optimized with the assistance of the present invention since outgoing connections for mobile CTX subscribers need not be routed via the CTX home switching center of the fixed network allocated to the mobile CTX subscriber. Standards that already exist such as, TCAP (transaction control application part), SCCP (signaling connection control part) or MTP (message transfer part), can continue to be used. The mobile radio standards only need to be slightly adapted, for example in view of the visitor data file (visitor location register VLR) or of the MAP (mobile application part).
In order to enhance the throughput of the inventive system, only the CTX-specific data that are actually required are transmitted via the above-described message interface into the public mobile radio telephone network or to the mobile switching center. These relevant CTX-specific data are usually feature or function indicators that specify the available CTX functions, and also comprise address information. Extensive CTX group data such as the CTX group number plan, by contrast, need not be transmitted.